Abstract: Expanded Polystyrene (EPS) beads lightweight soil is a new type of artificial geotechnical material with low density and high strength, to promote the wide application of EPS beads lightweight soil in the project, replacing some cement with fly ash as a curing agent, which can consume the waste fly ash and reduce the cost of the project. EPS beads were used as a lightweight material, and cement and fly ash were used as curing agents into the raw soil to make fly ash EPS lightweight soil. The EPS beads contents are 0.5%, 1%, 1.5%, and 2%, the total curing agent contents are 10%, 15%, 20%, and 25%, and the proportions of cement replaced by fly ash are 0%, 15%, 30%, 45%, and 60%, respectively. Unconfined compressive strength (UCS) test and scanning electron microscopy (SEM) test were conducted. The results show that the EPS content, the total curing agent content, and the proportion of cement replaced by fly ash have a significant impact on the UCS of lightweight soil. It decreases with an increase in the EPS content, increases with an increase in the total curing agent content, and decreases with an increase in the proportion of cement replaced by fly ash. When the proportion of cement replaced by fly ash is not too high, the strength of lightweight soil decreases less, and its performance can still meet the engineering needs. At the same time, it can also consume fly ash and reduce environmental pollution. EPS lightweight soil mixed with fly ash still has advantages, and it is recommended that the proportion of cement replaced by fly ash is controlled to less than 30%. The failure patterns of lightweight soil mainly include splitting failure, oblique shear failure and bulging failure, which are related to the material mix ratio.
